The present invention relates to an umbilical for transmission of fluids and electric current/signals between the sea surface and equipment located on the sea bed, in particular in deep waters, comprising a number of pipes and electric conductors/wires collected in a bundle, a filler material arranged at least partly around and between the pipes and conductors/wires, and a protective sheath enclosing the pipes, conductors/wires and filler material.
Umbilicals of this type are constructed as a composed structure which is able to transfer hydraulic liquids, chemicals, fluids, electric and optical signals and electric power between equipment on the sea bed and on the sea surface. An early version of such umbilicals is known from WO 93/17176. Typical for this umbilical is that most of the load transfer takes place in a centrally located steel pipe of substantial dimension. Further examples of prior art are disclosed in GB 2 326 177 A and GB 2 326 758 A, all having the same assignee as the present invention.
An International patent application no. PCT/N005/00215 related to a power umbilical is simultaneously filed.
The above mentioned heavy section steel pipes add substantial weight to the umbilical due to their own weight. The pipes need to have such large dimensions just because they act as load carrying elements, and not because the transported medium requires this. Thus the sea depth to which the umbilical having the traditional construction can be used is limited.
Instantly, it appears that steel rope could be used as load carrying elements. This, however, does not solve the problem to a considerable extent. Steel rope also add substantial weight and in combination with heavy pipes, one does not reach large depths before the umbilical achieves yield stresses and is torn off due to its own weight.
Substantial efforts and resources have been used in order to find a solution on how to be able to use these umbilicals down to the sea bed at real large sea depths, such as 2500 meters and more.
This is now solved by combining a technology that is developed by the assignee of the present invention, viz. the technology that is used for tension legs of floating platforms. See for example WO 02/057560 A1.
Thus, according to the present invention an umbilical of the introductory said kind is provided, which is distinguished in that the umbilical comprises separate load carrying elements, which load carrying elements are light weighted rods of composite material. The light weight rods of composite material may preferably be carbon rods having embedded strength fibers. The rods can either be collected in bundles or appear individually or in a combination thereof.
Composite material has that excellent property that the material has approx. the same load carrying capacity as steel, at the same time as the weigh is reduced to about 10% of that of steel. Thus the load carrying elements do not contribute substantially to the total weight of the umbilical which thereby provides an option to use the umbilical in deep waters. One may get so much deeper as the weight reduction allows. A typical example of composite material is carbon rods having embedded strength fibers.
In one embodiment the filler material, the pipes and conductors/wires can be laid in a helix or spiral configuration about the longitudinal axis of the umbilical.
In a second embodiment the filler material, the pipes and conductors/wires can be laid in a substantially rectilinear configuration without any essential twisting or spiraling.
The load carrying elements can be collected in a twisted or spiraling bundle that is located centrally as a core element within the umbilical.
As an alternative the load carrying elements of the umbilical can be distributed to a number of bundles located peripheral relative to the longitudinal axis of the umbilical.
As an alternative the umbilical can also include weight elements in order to ad mass/weight to the umbilical, either in all its extent or in some sections.
The filler material, the pipes and the conductors/wires can be laid in several layers viewed in radial direction.
In one embodiment the load carrying elements can consist of single rods that are distributed within the transversal cross section, and some may possibly be located adjacent to each other without thereby being collected in a bundle.
Even if not strictly necessary, the filler material will in a suitable embodiment be in the form of elongated channel elements that are able to at least partly enclose the respective pipes and cables in order to keep these in position relative to each other.
Other and further objects, features and advantages will appear from the following description of preferred embodiments of the invention, which are given for the purpose of description, and given in context with the appended drawings where: